This invention relates to a gas carbon engine power unit and in particular to a gas turbine engine power unit which is arranged to operate in first mode of operation in which its power output is of a given magnitude and in a second mode of operation in which its power output is boosted to a higher magnitude.
It is known from, for instance GB651319 and GB2199083A, to provide gas turbine engine power units which are arranged to operate in a first, conventional mode of operation and in a second mode of operation in which their output power is boosted when compared to that of their first mode of operation. Such power units comprise a conventional gas turbine engine gas generator and a power turbine driven by that generator. In the conventional mode of operation, the gas efflux from the power turbine is directed to a heat exchanger which places the hot gas efflux in heat exchange relationship with compressed air within the gas turbine engine gas generator prior to that air being directed into the engine's combustion equipment. The gas efflux originating from the power turbine is directed through non-operative combustion equipment to a further turbine which drives a supplementary air compressor which in turn supplies pressurised air to the gas turbine engine gas generator.
In the boosted mode of operation, the heat exchanger is by-passed and the power turbine gas efflux is directed to the now operative combustion equipment. The resultant combustion products then expand through the further turbine which drives the supplementary air compressor at an increased rate, thereby boosting the amount of air supplied to the gas turbine engine gas generator and in turn the power output of the power turbine driven by the gas generator.
The power units of GB651319 and GB2199083A are depicted in diagrammatic form and do not address the problems of constructing an actual power unit in which the efficiency of the unit is maintained at acceptable levels by minimising aerodynamic and thermodynamic losses. Moreover they do not address problems associated with the provisions of constructing a power unit which is sufficiently compact to be located in a vehicle, such as a marine vessel or land vehicle, in which the space available for a power unit is limited.